Abstract
After discussing the basic properties of life and origin on Earth (which is still debatable) we highlight the role played by earth in protecting life, especially complex life. The atmosphere protects life on the Earth’s surface from short wavelength radiation, the Earth’s magnetosphere provides a shielding against energetic charged particles. Life even exists under extreme conditions on Earth. We have already discussed black smokers in the context of origin of life and we will give further examples of life existing in at first sight hostile conditions. The study of extremophiles has enhanced the chance to find life elsewhere under extreme environments such as on the surface of Mars. The main message of this chapter is that life is being found to exist in environments that have been thought as hostile several decades ago which gives us hope that the extension of a habitable zone might be broader.
